Objectives: 1) To explore the action spectrum for photochemical and thermal damage more thoroughly, especially towards the ultraviolet to find peak wavelength for retinal damage. 2) To investigate the site or sites of photochemical damage to the retina by histochemical, pathological and electron microscopy techniques. 3) To use animals (rhesus monkey) trained to a visual acuity task to determine the extent of damage to visual acuity by mild or threshold photochemical lesions of the retina and to study the rate of recovery, if any. Upon sacrifice eyes of said animals will be examined by electron microscopy to correlate pathology with loss of visual acuity. 4) To experiment on the feasibility of exposing unanesthetized animals to repetitive daily radiant fluxes of light. 5) To collect threshold data on diabetic retinopathy patients. 6) To collect and analyze data on absorptance and reflectance in the retina. Also, to study effects of body temperature on threshold photochemical lesions. 7) To investigate the effects of retinal spot size on the photochemical threshold lesion. Bibliographic references: W.T. Ham, Jr. Remarks on Fundus Reflectance. Accepted for publication in Vision Research (Corrected galley sent back to editor 6 June 1975); W.T. Ham, Jr., H.A. Mueller, R. Peterson & r. James. Thermal vs Photochemical Retinal Radiation Damage. Paper presented at annual ARVO meeting, Sarasota, Fla., 2 May 1975.